The present invention relates to an intake valve control system and method for an internal combustion engine.
A throttle valve is disposed in an intake passage of an internal combustion engine (e.g. gasoline engine) so as to regulate an intake air quantity of the engine according to an opening of the throttle valve for engine load control. This throttle intake control structure is likely to subject to a relatively large pumping loss in a low/middle engine load range where the throttle valve opening is relatively small. There is hence alternatively proposed a throttleless intake control structure to regulate engine intake air without the use of a throttle valve as in the case with a diesel engine.
For example, Japanese Laid-Open Patent Publication No. 11-107725 proposes an intake valve control system for an internal combustion engine, which includes a variable valve mechanism capable of continuously increasing or decreasing intake valve operation angle and lift of the engine to regulate an intake air quantity without reference to throttle opening control.
Japanese Laid-Open Patent Publication No. 2003-74318 proposes an intake valve control system for an internal combustion engine, which includes a first variable valve mechanism capable of continuously increasing or decreasing intake valve operation angle and lift of the engine and a second variable valve mechanism capable of continuously advancing or retarding an intake valve maximum lift phase of the engine. The first and second valve mechanisms are operated independently of each other to vary the intake valve lift characteristics and regulate an intake air quantity without reference to throttle opening control.
Japanese Laid-Open Patent Publication No. 2002-89303 proposes an internal combustion engine having an intake valve control system of the above-proposed type, to decrease intake valve operation angle and lift of the engine to adequate levels at the time of engine stop so as to reduce a valve driving force for the next engine start.
These intake valve control systems allow wide-throttle or throttleless engine running in a low engine load range to achieve a significant reduction in pumping loss. These intake valve control systems also allow precise intake control by adjusting the intake valve operation angle and lift to very small levels during idling.